U.S. patent application number 10/642603 was filed with the patent office on 2004-10-14 for ball screw actuator for aircraft control surfaces.
This patent application is currently assigned to UMBRA CUSCINETTI S.P.A.. Invention is credited to Capolungo, Sandro, Perni, Federico, Pizzoni, Luciano.
Application Number | 20040200929 10/642603 |
Document ID | / |
Family ID | 29765761 |
Filed Date | 2004-10-14 |
United States Patent
Application |
20040200929 |
Kind Code |
A1 |
Perni, Federico ; et
al. |
October 14, 2004 |
BALL SCREW ACTUATOR FOR AIRCRAFT CONTROL SURFACES
Abstract
A ball screw actuator for aircraft control surfaces comprises a
lead screw, motor means to set the screw in rotation about its
longitudinal axis and a primary body connected to a control surface
and engaged on the control screw by means of a plurality of balls
movable on the thread of said screw. A secondary body is connected
to the primary body and has an auxiliary portion provided with an
engagement surface facing the thread of the lead screw at a
predetermined distance; the engagement surface is shaped to engage
on the thread of said lead screw. The actuator further comprises
means for uncoupling the secondary body from the auxiliary portion
in the rotation motion about the longitudinal axis.
Inventors: |
Perni, Federico; (Trevi,
IT) ; Capolungo, Sandro; (Torgiano (PG), IT) ;
Pizzoni, Luciano; (Foligno (PG), IT) |
Correspondence
Address: |
YOUNG & THOMPSON
745 SOUTH 23RD STREET 2ND FLOOR
ARLINGTON
VA
22202
|
Assignee: |
UMBRA CUSCINETTI S.P.A.
FOLIGNO
IT
|
Family ID: |
29765761 |
Appl. No.: |
10/642603 |
Filed: |
August 19, 2003 |
Current U.S.
Class: |
244/99.11 ;
244/99.2 |
Current CPC
Class: |
F16H 25/2204 20130101;
F16H 25/205 20130101; F16H 25/2472 20130101 |
Class at
Publication: |
244/075.00R |
International
Class: |
B64C 015/00 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 11, 2003 |
IT |
RM2003A000169 |
Claims
1: Ball screw actuator for aircraft control surfaces, comprising: a
lead screw having a thread; motor means to set the screw in
rotation about its own longitudinal axis; a primary body connected
to a control surface and engaged on the lead screw by means of a
plurality of balls movable on the thread of said screw; a secondary
body connected to the primary body and having an auxiliary portion
provided with an engagement surface facing the thread of the
control screw at a predetermined distance; the engagement surface
being shaped to engage the thread of said lead screw; wherein it
further comprises means for de-coupling the secondary body from the
auxiliary portion in the rotation motion about the longitudinal
axis radially interposed between said secondary body and said
auxiliary portion; with the secondary body de-coupled from the
auxiliary portion, said auxiliary portion being free to rotate
together with the screw with respect to the secondary body upon any
rotation of the screw.
2: An actuator as claimed in claim 1, wherein the means for
de-coupling the secondary body from the auxiliary portion
comprising at least a weakened portion for connecting the secondary
body and said auxiliary portion.
3: An actuator as claimed in claim 2, wherein the means to
de-couple the secondary body from the auxiliary portion comprise
friction reducing means radially interposed between said secondary
body and said auxiliary portion.
4: An actuator as claimed in claim 1, wherein the auxiliary portion
has a tubular shape coaxial to the lead screw.
5: An actuator as claimed in claim 4, wherein the engagement
surface of the auxiliary portion with tubular shape internally has
an inverse thread adapted to engage the thread of the lead
screw.
6: An actuator as claimed in claim 2, wherein the weakened
connecting portion is a pin inserted in the auxiliary portion and
in the secondary body.
7: An actuator as claimed in claim 3, wherein the friction reducing
means have at least a bearing.
8: An actuator as claimed in claim 3, wherein the secondary body
coaxially surrounds the auxiliary portion.
9: An actuator as claimed in claim 8, wherein the friction reducing
means have at least a bearing interposed between the secondary body
and the auxiliary portion.
10: An actuator as claimed in claim 8, wherein the friction
reducing means have two bearings set side by side and interposed
between the secondary body and the auxiliary portion.
11: An actuator as claimed in claim 8, wherein the weakened
connecting portion is a pin inserted in the secondary body and in
the auxiliary portion.
12: An actuator as claimed in claim 8, wherein the secondary body
has: a first tubular body radially distanced from the auxiliary
portion, to define a containment chamber for at least a bearing
defining said friction reducing means; a second tubular body
coaxial and integral with the first and radially approached to the
auxiliary portion.
13: An actuator as claimed in claim 12, wherein the weakened
connecting portion is a pin inserted into the second tubular body
of the secondary body and into the auxiliary portion.
14: An actuator as claimed in claim 1, wherein at least the
engagement surface of said auxiliary portion is made of material
with high friction coefficient.
15: An actuator as claimed in claim 1 wherein at least the
engagement surface of said auxiliary portion is made of low
friction material.
16: An actuator as claimed in claim 1, wherein the primary body is
directly connected to the secondary body.
17: An actuator as claimed in claim 16, wherein the secondary body
is connected to the primary body about an axis orthogonal to the
longitudinal axis of the lead screw.
18: An actuator as claimed in claim 1, wherein the primary body
forms a single body with the secondary body.
19: An actuator as claimed in claim 1, wherein the secondary body
is directly connected to the control surface.
20: Ball screw actuator for aircraft control surfaces, comprising:
a lead screw having a thread; motor means to set the screw in
rotation about its own longitudinal axis; a primary body connected
to a control surface and engaged on the lead screw by means of a
plurality of balls movable on the thread of said screw; a secondary
body connected to the primary body and having an auxiliary portion
provided with an engagement surface facing the thread of the
control screw at a predetermined distance; the engagement surface
being shaped to engage the thread of said lead screw; the secondary
body being engageable to the screw only through the engagement
surface of said auxiliary portion; wherein it further comprises
means for de-coupling the secondary body from the auxiliary portion
in the rotation motion about the longitudinal axis radially
interposed between said secondary body and said auxiliary portion;
with the secondary body de-coupled from the auxiliary portion, said
auxiliary portion being free to rotate together with the screw with
respect to the secondary body upon any rotation of the screw.
21: Ball screw actuator for aircraft control surfaces, comprising:
a lead screw having a thread; motor means to set the screw in
rotation about its own longitudinal axis; a primary body connected
to a control surface and engaged on the lead screw by means of a
plurality of balls movable on the thread of said screw; a secondary
body connected to the primary body and having an auxiliary portion
provided with an engagement surface facing the thread of the
control screw at a predetermined distance; the engagement surface
being shaped to engage the thread of said lead screw; the auxiliary
portion being integral with the secondary body along the
longitudinal axis; the secondary body being engageable to the screw
only through the engagement surface of said auxiliary portion;
wherein it further comprises means for de-coupling the secondary
body from the auxiliary portion in the rotation motion about the
longitudinal axis radially interposed between said secondary body
and said auxiliary portion; with the secondary body de-coupled from
the auxiliary portion, said auxiliary portion being free to rotate
together with the screw with respect to the secondary body upon any
rotation of the screw, preventing any axial motion of said
secondary body.
Description
BACKGROUND OF THE INVENTION
[0001] The present invention relates to a ball screw actuator for
aircraft control surfaces. Aircraft control surfaces are commanded
by appropriate actuators able to move them between two extreme
positions, in such a way as to make the surfaces assume operative
configurations suitable for specific phases of flight. For example,
actuators are used to command the flaps installed on the trailing
edge of a wing or to control the elevators mounted on the tail
empennage.
[0002] Ball screw actuators are known which are constituted by a
lead screw set in rotation about its own longitudinal axis by a
motor and associated to a tubular body, known in the specific art
as lead nut, mounted coaxially on the screw itself. The lead nut is
cinematically connected to the control surface whilst the screw is
mounted integrally on the load bearing structure of the aircraft.
The lead nut, which is prevented from rotating, has on its own
inner surface appropriate seats for a plurality of balls able to
rotate on themselves and to slide in the throat of the thread of
the lead nut. The rotation of the lead screw determines, by means
of the coupling provided by the screws, the sliding of the lead nut
along the longitudinal axis of the screw and the consequent motion
of the control surface.
[0003] Also known are actuators in which the screw is connected to
the control surface and translates, whilst the lead nut is
connected to the structure and rotates. Since in the aeronautical
field it is necessary to guarantee a very high safety margin to the
structures, or put the aircraft at risk of crashing, prior art
actuators are provided with particular devices to prevent control
surfaces from becoming uncontrollable due to a failure in the lead
nut or lead screw.
[0004] The loss of the balls of the lead nut or the rupture thereof
leads to the loss of the structural continuity between the controls
and the controlling surfaces, since the lead nut is free to slide
relative to the screw. In this situation, the surfaces are free to
move under the action of aerodynamic and inertial forces and the
aircraft is absolutely uncontrollable.
[0005] To overcome this drawback, known actuators have been built
which comprise an auxiliary lead nut, connected to the main one,
which becomes operative when a malfunction occurs in the main lead
nut itself. The auxiliary lead nut serves as a safety device.
[0006] For instance, auxiliary ball lead nuts are known which are
structurally similar to the primary ones. Although this type of
solution assures control even after the rupture of the main lead
nut, it should be noted that auxiliary lead nuts can be subject to
the same type of failure as the primary ones.
[0007] Also known are inverse thread auxiliary lead nuts
constituted by a tubular portion connected to the main lead nut
which has on its own inner surface, facing the lead nut, a thread
with reversed shape relative to the thread of the screw.
[0008] During the proper operation of the main lead nut, the balls
maintain the reversed thread of the auxiliary lead nut at a
determined distance from the thread of the screw and the tubular
portion of the is perfectly coaxial to the longitudinal axis of the
screw.
[0009] As a result of the loss of the balls caused by a failure,
both lead nuts lose the coaxial positioning relative to the shaft
of the screw and the inverse thread of the auxiliary lead nut is
engaged in the throat of the thread of the lead nut.
[0010] A first type of inverse thread auxiliary lead nut is made of
frictionless material which slides in the throat of the thread of
the screw and serves the function of the balls for a certain
fraction of the required working life. The main drawback of such a
solution is that the duration of the frictionless inverse thread
cannot be estimated correctly; the thread can be damaged rapidly
and lead to the lack of structural connection between the
aforementioned components.
[0011] Auxiliary lead nuts are known with high friction coefficient
which causes the seizure of the auxiliary lead nut on the screw and
the consequent locking of the main lead nut and of the control
surfaces connected thereto. The control surfaces are no longer
controllable, but remain motionless in a determined position,
allowing in any case to control the aircraft to a landing.
[0012] The seizure of the inverse thread on the screw occurs during
the rotation thereof. The torque imparted to the screw by the motor
is contrasted by the friction torque imparted by the inverse thread
under the action of the external load. Consequently, the load at
which the seizure occurs may be very high and not included in the
flight envelope of the aircraft.
[0013] Also known from the document U.S. Pat. No. 6,467,363 is a
device for blocking a ball screw actuator, which comprises a sensor
mechanism, able to detect a malfunction of the primary lead nut,
and means for blocking the screw relative to the primary lead nut
in case of failure. The locking means are defined by a pair of
disk-shaped elements which, activated by the sensor mechanism, are
thrust by respective springs between the throat of the thread of
the screw and an inner surface of a containment body of the screw
itself. This device is formed by a multiplicity of elements easily
subject to rupture which cannot assure the necessary safety
margin.
[0014] Lastly, the document U.S. Pat. No. 4,644,811 has a ball
screw actuator provided with a free wheel end stop device. The
actuator comprises a ball screw threaded on a predominant portion
except at one of its ends. The screw is inserted in a main lead
nut, provided with balls engaged on the thread of the screw, and in
a secondary lead nut, integral with the main one and driven
thereby. The secondary lead nut is coupled with the main one by
means of a retaining pin and a thrust bearing interposed
axially.
[0015] When the main lead nut exits the threaded portion of the
screw and tends to continue its own run, the secondary lead nut is
engaged on the thread of screw and tends to rotate with the screw
itself breaking the retaining pin. This device allows the lock the
lead nut only at the end of the run.
SUMMARY OF THE INVENTION
[0016] An aim of the present invention is to solve the problems
noted in the prior art, proposing a ball screw actuator for
aircraft control surfaces able to overcome the aforementioned
drawbacks. In particular, an aim of the present invention is to
provide a ball screw actuator for aircraft control surfaces that
assures the ability of controlling the aircraft even in case of
failure of the main lead nut.
[0017] Another aim of the present invention is to propose a simple
and reliable ball screw actuator for aircraft control surfaces.
[0018] A further aim of the present invention is to obtain an
actuator provided with a safety device that operates at low loads,
to prevent further damages to the devices and allow the nearly
complete recovery of the parts that comprise it.
[0019] These aims and others besides, which shall become more
readily apparent in the course of the present description, are
substantially achieved by a ball bearing actuator for aircraft
control surfaces comprising the characteristics expressed in one or
more of the accompanying claims.
BRIEF DESCRIPTION OF THE DRAWINGS
[0020] Further characteristics and advantages shall become more
readily apparent from the detailed description of a preferred, but
not exclusive, embodiment of a ball bearing actuator for aircraft
control surfaces in accordance with the present invention. The
description shall be provided below with reference to the
accompanying figures, provided purely by way of non limiting
indication, in which:
[0021] FIG. 1 schematically shows a cross section of a control
surface of an aircraft connected to an actuator in accordance with
the present invention;
[0022] FIG. 2 shows an enlarged, partially sectioned view of the
actuator of FIG. 1, in a first operative condition (normal
operation); and
[0023] FIG. 3 shows a portion of the actuator of FIG. 2 in a second
operative condition (operation in failure condition).
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0024] With reference to the accompanying figures, the number 1
globally designates a ball screw actuator for aircraft control
surfaces according to the present invention.
[0025] In the illustrated embodiment, the actuator 1 is housed
within a structure 2 of the aircraft, for instance the tail boom,
and commands the movement of a control surface 3, for example the
stabilizer of the tail plane. The stabilizer 3 is moved by the
actuator 1 about its own hinge axis 4, to change its own angle of
attack.
[0026] The actuator 1 comprises a lead screw 5 which is moved in
rotation about its own longitudinal axis 6 by motor means 7, known
and therefore illustrated only schematically in FIG. 1, connected
to the to the pilot's controls.
[0027] On the lead screw 5 is mounted a primary body 8, which in
the specific technical field goes under the name of lead nut,
coupled to the thread 9 of the screw 5 by means of a plurality of
balls 10.
[0028] In particular, as FIG. 2 shows, the primary body 8, tubular
shaped, has an inner surface 11 provided with seats 12 for the
balls 10. The balls 10 are located in the throat 13 of the thread 9
and constitute the structural connection between the screw 5 and
the nut 8. The balls 10 also keep at a certain distance the planar
crest 14 of the thread 9 from the inner surface of the primary
organ 8.
[0029] The rotation of the screw 5 relative to the primary body 8
about the longitudinal axis 6 causes the balls 10 to slide in the
throat 13 of the thread 9 of the screw 5 and the primary body 8 to
move axially relative to the screw 5.
[0030] In the embodiment shown in FIG. 1, the screw 5 is mounted by
means of a primary support body 15 on the structure 2 of the
aircraft and the primary body 8, connected to the control surface
3, slides along the longitudinal axis 6 of the screw 5. The support
body 15 is pivotally engaged to the structure 2 in correspondence
with a hinge 16.
[0031] In an embodiment not shown herein, the primary body 8 is
fastened to the support body 15 whilst the screw 5 slides axially
inside the lead nut. The control surface 3 is connected to an end
of the screw 5, for instance by means of an eyelet pivotally
mounted on said end.
[0032] The primary body 8 is connected to the control surface 3 by
means of redundant structural elements. With reference to the
preferred embodiment shown in FIG. 2, the primary body 8 has two
latching portions 17 which extend from opposite sides relative to
the longitudinal axis 6 of the screw 5. Each of the latching
portions 17 is engaged to the elevator 3.
[0033] By way of example, in the embodiment shown in FIG. 1, the
primary body 8 is hinged to the control surface 3, in
correspondence of its own latching portions 17, about a respective
hinge axis 18.
[0034] During operation, with reference to FIG. 1, the rotation of
the screw 5 in a direction or in the opposite one causes the
sliding of the primary body 8 away (arrow A1) from the support 15
or towards (arrow B1) the support body 15. The primary body 8,
moving away from the support body 15, causes the clockwise rotation
of the stabilizer 3 (arrow A2). The primary body 8, moving towards
the support body 15, causes the counter-clockwise rotation of the
stabilizer 3 (arrow B2).
[0035] The actuator 1 also comprises a secondary body 19 connected
to the primary body 8.
[0036] The primary body 8 can be directly connected to the
secondary body 19, as shown in FIG. 2, or even form a single body
with the secondary body 19 itself.
[0037] Alternatively, the secondary body 19 is connected directly
to the control surface 3 and the primary body 8 is fastened to the
secondary body 19 by means of the same control surface 3. In the
schematic representation of FIG. 1, the secondary body 19 is
connected by means of a hinge 20 to the control surface 3. The
hinge 20 is purposely constructed with a determined play so that,
during the normal operation of the actuator 1, the lead screw 5 and
the primary body 8 are allowed to rotate about their own hinge axis
18.
[0038] The secondary body 19 has an auxiliary portion 21,
preferably with tubular shape coaxial to the lead screw 5, provided
with an engagement surface 22 facing the thread 9 of the screw 5
and at a predetermined distance from the thread 9.
[0039] Preferably, the engagement surface 22 is shaped to engage
the thread 9. More in detail, the engagement surface 22, which
coincides with the inner surface of the auxiliary portion 21 with
tubular shape, has an inverse thread 23 shaped counter to the
thread 9 of the screw 5 and adapted to engage on the thread 9 of
the screw 5 itself (FIGS. 2 and 3). According to a first embodiment
and a first operating mode, which shall be described in detail
farther on, the engagement surface 22 of the auxiliary portion 21
is made of material with high friction coefficient.
[0040] In a second embodiment, the engagement surface 22 is made of
frictionless material.
[0041] Advantageously, the actuator 1 further comprises means 24
for uncoupling the secondary body 19 from the auxiliary portion 21
in the rotation motion about the longitudinal axis 6; said means
are radially interposed between the secondary body 19 and the
auxiliary portion 21.
[0042] In the preferred embodiment, the uncoupling means 24 have at
least a weakened portion 25 which connects the secondary body 19 to
the auxiliary portion 21 and, preferably, friction reducing means
26 interposed between the auxiliary portion 21 and the secondary
body 19.
[0043] Both the weakened portion 25 and the friction reducing means
26 work on the rotation motion between the two aforementioned
components.
[0044] The removal of the weakened portion 25 allows the relative
rotation between the secondary body 19 and the auxiliary portion 21
whilst the friction reducing means 26 facilitate said rotation. The
two bodies 19, 21 are instead axially integral.
[0045] Preferably, the weakened connecting portion 25 is a pin
inserted both in the secondary body 19 and in the auxiliary portion
21 whilst the friction reducing means 26 are defined by at least a
bearing, for instance a ball bearing, which, radially interposed
between the two bodies 19, 21, bears the loads in the direction of
the longitudinal axis 6. More in detail, the primary body 8 is
preferably constituted by a tubular portion, which bears the inner
surface 11 provided with the seats 12 for the balls 10.
[0046] The secondary body 19 coaxially surrounds the auxiliary
portion 21 and is connected, in the embodiment shown in FIG. 2, to
the primary body 8 about an axis 27 orthogonal to the longitudinal
axis 6 of the control screw 5. The friction reducing means 26 have
at least a bearing, preferably two bearings set side by side,
interposed between the secondary body 19 and the auxiliary portion
21. The pin 25 is preferably inserted between the secondary body 19
and the auxiliary portion 21.
[0047] In particular, the secondary body 19 has a first tubular
body 28 radially distanced from the auxiliary portion 21 and a
second tubular body 29 coaxial and integral to the first 28 and
radially approached to the auxiliary portion 21 (FIG. 3).
[0048] Between the first tubular body 28 and the auxiliary portion
21 is defined a containment chamber 30 in which are positioned the
two bearings 26 inserted in annular recesses 31, 32 obtained
respectively in the first tubular body 28 and in the auxiliary
portion 21, to prevent the axial motion of one part relative to the
other.
[0049] A ring nut 33 fastened to the auxiliary portion 21 axially
locks the bearings 26 and the auxiliary portion 21. In the
illustrated embodiment, the two bearings 26 are separated by
spacers 34 and, between the secondary body 19 and the auxiliary
portion 21, outside the bearings 26, are mounted two gaskets
35.
[0050] The second tubular body 29 and the end of the auxiliary
portion 21 approached thereto have respective coaxial holes 36, 37
for the insertion of the pin 25 which therefore is oriented
transversely relative to the longitudinal axis 6 of the screw 5.
The pin 25 exhibits a reduction of the section of its own stem 25a
which, once placed in the holes 36, 37 is positioned in
correspondence with the coupling surfaces between the second
tubular body 29 and the end of the auxiliary portion 21.
[0051] Lastly, in the embodiment illustrated in FIG. 2, the
secondary body 19 comprises two appendages 38 which extend towards
the primary body 8 and engage the two latching portions 17. Each of
the appendages 38 is formed by two arms 39 parallel to the
longitudinal axis 6 of the screw 5 and provided with respective
coaxial holes 40 into which is inserted one of the two latching
portions 17. The articulation axis 27 thus coincides with the axis
of the latching portion 17.
[0052] In another embodiment the secondary body 19 is connected to
the control surface in a manner that is wholly independent from the
primary body 8.
[0053] In operation, in the absence of failures, the primary body 8
moves on the screw 5 as specified above whilst the engagement
surface 22 of the auxiliary portion 21 remains distanced from the
thread 9 of the screw 5. The auxiliary portion 21 is not subject to
any rotation, since the pin 25 makes it integral with the secondary
body 19.
[0054] When the actuator 1 as a result of a failure loses the balls
10 or the structural continuity between the primary body 8 and the
control surface 3, the consequence is that a segment of the inverse
thread 23 of the engagement surface 22 couples with the thread 9 of
the screw 5 (FIG. 3).
[0055] Due to the high friction coefficient between the screw 5 and
the inverse thread 23, the screw 5, in its rotation about the
longitudinal axis 6, tends to drag with it the auxiliary portion 21
and causes the breakage of the pin 25 in correspondence with the
reduction of the section of the stem 25a.
[0056] After the breakage of the pint 25, the auxiliary portion 21
is uncoupled, in the rotation motion, from the secondary body 19
but remains integral with the same secondary body 19 along the
longitudinal axis 6. The bearings 26 bear the loads along the
longitudinal axis 6 of the screw 5 and the transverse loads caused
by the loss of the coaxial condition between the screw 5 and the
primary body 8 and secondary body 19.
[0057] The screw 5, set in rotation by a command from the pilot,
drags with it the auxiliary portion 21 which rotates freely.
Consequently, the rotation of the screw 5 does not determine the
axial motion of the secondary body 19, of the primary body 8, or
the motion of the control surface 3. The pilot is unable to move
the stabilizer.
[0058] Simultaneously, the aerodynamic forces acting on the control
surface 3 are not able to move it. The moment generated by the
aerodynamic about the hinge 4 of the control surface 3 unloads on
the secondary body 19. The component along the longitudinal axis 6
of the force imparted on the secondary body 19 axially thrusts the
auxiliary portion 21 but is unable to move it, since, along this
direction, it is integral with the screw 5.
[0059] The invention achieves important advantages.
[0060] First of all, the actuator according to the present
invention assures, following a failure, the immediate coupling of
the safety device and the locking of the control surfaces.
[0061] Moreover, the seizure of the auxiliary portion on the screw
and the separation, in the rotation motion, from the secondary body
takes place at known loads, substantially determined by the
strength of the connecting pin.
[0062] Since the pin can be designed with a rather low breaking
load, the actuator according to the present invention allows to
avoid further damage to the actuator and to recover nearly all of
the parts that compose it during repair operations.
[0063] Lastly, the actuator according to the present invention is
structurally simple and reliable.
* * * * *